1. Field of the Invention
The present invention is directed to a robotic workstation such as those useful in wafer processing.
2. Description of the Related Art
Robotic workstations are applied to numerous industries. In the data storage industry, they have been applied to magnetic disk testing, inspecting and processing. In the storage industry, robotic workstations are centered around a robotic arm operated by a programmable controller which moves disks from a fixture to testing stations placed proximate to the robotic arm. Typically, input disks are provided to a workstation by a human operator in a cassette or carrier and additional empty carriers are used for output disks, finished after the result of testing operations.
In conventional robot-based pick-and-place workcells, input and output is stowed in a specific static location. The robot travels to this location to pick parts and brings them to other machines, processors and/or stations in the work cell that perform some action on the part. Conversely, parts that are complete are retrieved from these stations, brought back to this static location and binned into fixtures for output. This motion contributes to the biggest percentage of the robot's cycle time, which is the metric for the speed and the potential or actual throughout of a robotic work cell.
Each robot includes an end effector which retrieves and settles disks in the fixtures. In the application of testing or processing rigid media such as magnetic disks, conventional workcells have a dual sided end-effector that holds two disks 180° apart. The robot moves to the machine to be serviced, removes the old disk, rotates its end-effector 180°, and brings the new part to the machine. Due to inertial constraints of the hardware, the fastest exchanges possible are around 2.0 to 2.4 seconds. During this time, the rest of machine sits idle. In addition, the 180° rotation requires that a volume of space above the machine be kept clear to avoid collision. This air-space requirement can cause problems when machines are packed tightly together in a workcell, as the robot may have to retreat to a safe location a short distance from the machine to perform the rotation, then go back to bring the new part to the machine. This degrades cycle time.
To combat this problem and improve performance, single sided, dual paddle, end effectors were developed. In general, these single ended end-effectors were attached to the robot's z-shaft at their center of rotation. Each paddle was on a pivot and could pitch down or pitch up, by means of a pneumatically actuated air cylinder. The reason for this pitch up/down requirement is that the cassettes carry the disks vertically while the spindles that test the disks require them to be rotated so that the disk surfaces are parallel to the floor and ceiling.
Generally, robots and end effectors perform a number of standard functions in relation to magnetic disk processing. These functions include first picking a disk from a fixture or cassette, whereby a paddle is pitched down, the robot positions it on top of the disk to be picked and the disk is retrieved into the paddle. Following this, the robot moves up and away from the test station. The robot can also go to a tester that just finished testing a disk. In this task, the robot pitches both paddles up and moves to the tester with the empty paddle. The robot can take the old disk in one paddle, in which case the paddle acquires the old disk and moves up over the spindle. The robot can put a new disk on. In a dual end effector system, to put the new disk on, the robot rotates the end-effector 180°, moves down and drops off the new disk on the spindle. Next, the robot can bin the old disk by moving toward the output cassette, pitching down the paddle with the completed disk, moves down into the slot and releases the disk.
Most of the prior art end-effectors had a somewhat compact body, with pneumatic actuation to pitch the paddles. The smaller the body, the longer the paddle pivot that was need and more vertical-stroke used in moving the end effector up and down to get disks on and off testers and cassettes.
An end effector developed by Phase Metrics Inc., included a slimmed down body making it very thin as compared to the previous versions. Doing this, and keeping the center-of-disk constant as compared to the dual sided, end-effector, resulted in much shorter pivot distances. This, along with the lighter weight and smaller rotational inertia resulted in much faster performance.
The only drawback to this end-effector, as compared to the dual end type, is that even when both paddles are pitched down, the distance is longer than the old end-effector. This requires more space in the workcell for the robot to move around so that it does not collide with various obstacles. These obstacles may be safety enclosures, tester components or the robot itself.
In some workcells, testers are arranged in a circle around the robot, each with its own safety enclosure/shield. When technicians take a testers offline to work on them, the safety shield is raised to protect them from the robot inadvertently attempting to access the space they are occupying. This shield unfortunately consumes some of the robot's work space and interferes with the end-effector when the robot is exchanging disks on an adjacent tester. In this case, the robot must take the old disk, move back to a safe point, pitch down both paddles and then move in to drop off the new part. This motion adds an extra 2.0 seconds to the exchange time.
Because robots and test stations are quite expensive, performance improvements to new and existing robot installations are crucial.